Branch line connector



July 2, 1957 v c, BENNETT 2,798,204

BRANCH LINE CONNECTOR Original Filed June 30, 1951 F' .1. 22 if I I I I 1 1/ \NVENTOR L'larg melifiemeli United States Patent-O ice BRANCH LINE CONNECTOR Clarence H. Bennett, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Continuation of application Serial No. 234,568, June 30, 1951. This application August 15, 1956, Serial No. 606,180 7 17 Claims. (Cl. 333-6) Thisapplication is a continuation of application Serial No. 234,568, filed June 30, 1951, now abandoned.

The present invention is related to coaxial lines and vision installations for apartment houses, the signal from the antenna may be applied to a feed or main coaxial line which passes through several apartments or rooms. At each point along the cable where it is desired to con nect a television receiver, \a bridging connection, or branch connection is'made with the main line, except perhaps at the end of the main line. Such branch connections involve making a connection with the feed line inner conductor and'another with the feed line outer conductor. Usually a resistor is inserted in series with the connection to the inner conductor to increase the impedance presented by the branch line to the main line. This increased impedance prevents any single branch line from withdrawing more than a desired proportion of the energy from the main line, so that there will be available energy to be fed from the main line to other branch lines connected to the main line at points more distant from the antenna than this single branch line.

Heretofore, making such branch line connections has involved a considerable amount of hand labor. Further, due to the cold flow of certain materials commonly used as the solid inner dielectric between inner and outer conductors, the feed line inner conductor connection may be soldered. However, preferably the inner conductor connection is spring loaded. Spring loading, as pointed out in the copending application of B. L. Brady, entitled Bridging Connection, Serial No. 151,270, [filed March 22, 1950, now issued as Patent No. 2,677,108, avoids the cold flow of the inner dielectric from releasing the contact at the feed line inner conductor after a time. The method and connector of the said Brady application affords a saving in skilled labor over prior methods.

- It is an object of the present invention to provide an improved connector of the general spring-loaded type disclosed in the said Brady application.

A further object of the invention is to reduce the cost of making branch coaxial cable connections.

'- Anotherobject of the invention is to make a branch connection with a feed coaxial line which is economical of labor in making the connection.

Another object of the invention is to provide aconnector requiring no special tools for applying the connector and making the connection.

A further object of the invention is to provide such a connector which ischaracterized by low reflection losses.

A further object of the invention is to provide a connector for making such a branch connection which connector is rugged, easily manufactured, has parts readily standardized for different sizes of cables, and may alford a standardized outlet to be connected to a further length 9f branch cable.

. is also bored and is counterbored at the end fitted into 2,798,204 Patented July 2, 1957 'A preferred connector in accordance with the inven tion has a metallic clamp to hold the main coaxial cable. The clamp preferably has metallic points driven into positive contact with the main cable outer conductor on applicaticn of the clamp. There is provided a pin having a head held loosely in a dielectric axially bored bolt. The pin is arranged coaxially with the bolt with its point protruding through an elongation or protrusion of the bolt. The clamp is threaded to receive the bolt with the axis of bolt and pin aligned to pass through the inner conductor of the clamped main cable. When the bolt is screwed into place, the point of the pin with the bolt protrusion is forced through the clamped cable outer conductor and inner dielectric between inner and outer conductors. A shoulder of the bolt serves as a stop to stop the bolt at the point where the protruding pin point just makes firm contact with the main cable inner conductor. The-protrusion now shields the pin from contact with the main cable outer conductor. The axial bore is counterbored from the top of the bolt to receive a resistor, with one'resistor terminal extending through the bore to bear against the pin head. The resistor is held in place by a spring, Inadvertent separation of pin and bolt is prevented by the assembly. However, due to the loose holding of the pin by the bolt, the pin is now free to be spring-loaded against the main cable inner conductor. Connections of the other resistor terminal and of the main cable cuter conductor are completed respectively through the spring and metallic clamp to a conventional coaxial line end-to-end connector.

In another embodiment, the resistor is held in the bolt assembly with one resistor terminal extending through the bolt projection to serve as pin.

The foregoing objects and other objects, advantages, and novel features of the invention will be more fully understood from the following description when taken in connection with the accompanying drawing in which like reference numerals refer to like parts and in which:

Fig. 1 is a longitudinal cross-sectional view of one embodiment of the invention;

Fig. 2 is a transverse cross-sectional view of the embodiment of Fig. 1 along the lines 2-2;

Fig. 3 is an enlarged transverse cross-sectional view of a portion of the embodiment of Fig. 1 showing the dielectric pin and bolt assembly more clearly; and

Fig. 4 is a partial enlarged transverse cross-sectional view similar to the view of Fig. 3, but of another embodiment of the invention in which one of the resistor ter minals serves as a pin.

Referring to the drawing, a housing 10 encloses a metallic clamp 12 comprising two parts, designated inner part part 14 and outer part '16 for convenience. The inner and outer parts are apertured to receive snugly screws 18 threaded to housing 10 to draw together the parts '14, 16 of the clamp. The parts 14, 16 are hollowed to grasp tightly'between them when drawn together by screws 18 a main coaxial line 20 to which a branch connection is made. The main coaxial line 20 has an inner conductor 22, an outer conductor 24, an inner dielectric 26 between inner and outer conductors 22 and 24, and an outer dielectric 28 to protect the outer conductor '24. The clamp inner part 14 has contact points 30 pressed through outer dielectric 26 and into contact with the outer conductor 28. Either the outer clamp part 16 may have similar points (not shown) or both parts may have such points.

The clamp inner part 14 is threaded to receive a dielectric bolt 32 which is axially bored and counterbored on both ends, one end having a head 34. A dielectric protrusion36 is fitted into the counterbored portion at the end of bolt 32 remote from head 34. The protrusion 36 the bolt 32, the diameter of the counterbore chamber 42 of protrusion 36 being somewhat larger than the diameter of the head 38 of a metallic pin 40. The pin head 38 is somewhat larger in diameter than the-bore in bolt 32, and is thus held loosely in chamber 42 with the :body of pin 40 extending throughthe bore of p rotrusion 36 and the pin point 44 extending beyond the termination of protrusion 36. Whenassembled, the protrusion 36 may be considered as part ofbolt 34, and is; affixed thereto, for example, either by the tight fit of-the protrusion head into the counterbored bolt or by the use of some suitable adhesive to bind the partstogether, or both. The bore in bolt 32 and protrusion 36 are coaxial with pin 40. v t

A dielectric post 46 is mounted on-a top .66 of frame ltiheld to the frame with screws 68. Post 46 is spaced from the clamp to one side of and near the bolt head 34. The post 46 is held to frame by a screw 60, which passes :through a slot in the spring and holds a washer 48 so that a metallic spring 52 is held or anchored to the post 46 but insulated from frame 10. The spring 50 has a detent54 to receive one terminal of a resistor (as shown), thedetent being substantially aligned with the axis of the bore of the bolt 34 assembly. The spring 52 extends in a plane normal to this axis from the post 46 to the axial line of a conventional coaxial end-to-end conmeter 56, where an upturned ear 58 is connected (only by spring pressure if desired, or by solder) to the inner conductor of end-to-end connector 56. The outer conductor of end-to-end connector 56 is connected rigidly to the frame 10. The end-to-end connector is threaded (internally or externally) to receive a mating end-to-end connector. Such end-to-end connectors are conventional and need not be further described.

In applying the branch connection of the invention, the inner and outer parts 14 and 16 of the frame 10 come assembled from the factory with the screws 18 loose. The main coaxial line 20 is laid in place within the groove or cylindrical portion 62 of the inner part 14. The outer part is then put into place with the grooved or bent portion 64 of the outer part 16 under the main line 2-0. The screws 18 are then tightened firmly, which causes the contact points 30 to make contact with the main line outer conductor 24, and also cradles themain line 20 firmly with its axis and inner conductor 22 substantially in alignment with the axis of the main clamp inner part.

The dielectric bolt 34 may be shipped from the factory loose or withdrawn before the main line 20 is clamped in place. The bolt 32 now inserted, and run down into place so that the head 34 is seated firmly. The bolt 32 when driven into place causes the pin point 44 and the protrusion 36 to be driven into main cable. The shoulder of the bolt 32 sets as a stop to prevent the pin point 44 from being driven through or damaging the main line inner conductor 22, the dimensions of the various parts being calculated for this purpose. Accordingly, the pin point 44 now bears against the inner conductor 22.

A resistor 70 of proper resistance value is now selected. This may be a standard resistor, with the leads closely clipped. The resistor 70 is inserted with one lead bearing against pin head 38. Next, the top 66 is atfixed'to the frame with the other resistor 70 terminal held in the detent 54. As the screws 68 are tightened, the spring 52 exerts pressure against the resistor 70 terminals and spring loads the contacts made by the spring 54 against the resistor terminal, by the other resistor terminal against pin head 38 and by the pin point 44 against themain cable inner conductor 22. The spring also takes up any cold flow in the material of the inner dielectric which might tend to release inner conductor 22 from good electrical contact with pin point 44. The protrusion 36 shields pin 40 to prevent contact of the pin 40 with the outer conductor, helps pierce the main line 20, and maintains the pin .in proper alignment. It .hasbeeniound;alsothat the inner dielectric, when made of polystyrene or the like, cold-flows around the protrusion 36, around the pin point 44, and between the pin 40 and the protrusion bore, thereby sealing the inner contact perfectly against moisture.

The frame 10 may now be inserted in a terminal box 72, only part of which is shown, which has a suitable cover plate (not shown) to cover the box 72, and leaves exposed only the cover plate and enough of the end-toend connector to connect with the mating end-toend connector.

The saving in labor over prior methods of making branch connections by the connector of the invention are appreciable. No particular skill is required, only reasonable care to see to it that the main line is properly cradled in between the clamp parts so that it is held in alignment to be pierced by the pin 40 to make contact with the main line inner conductor 22. No special tools are required to apply the connector and make the connection. An ordinary screw driver and wrench are sufficient. The bolt may be slotted to receive a screw driver and then eventhe wrench may be dispensed with.

In addition to the simplification oflabor made possible by the connector, it has been found that there are only minor reflections. of energy in themain cable from the contact point. This low reflection and attendant. low energy loss are probably due to the fact that the line discontinuity created by the small protrusion is very small, compared, for example, to atap-off connection made in conventional way by stripping the outer conductor and making solder connections. It has. also been found that the connector may be removed, and the disruption of the I main coaxial cable is so slight that its electrical characteristics are unimpaired. Several such connections may be successively made over the same short. section of main cable without appreciable damage thereto.

Some of the dimensions of a typical connector of the invention with a typical coaxial line having a nominal impedance of ohms to which connection is to be made are shown. The main line outer conductor 24 is braided copper; the inner conductor 22 is copper wire. The outer dielectric 28 is Vinylite (a rubber-like plastic) and the inner dielectric 26 is a low loss dielectric, polyethylene. The inner clamp part 14 may be made of zinc casting,- andfthe outer part 16 stamped from sheet metal. The dielectric bolt 32 may be made of low loss phenolic resin, such as that sold under the name Bakelite, the pin 40 of bronze. The post 46 may be made of the same low loss resin, and the spring 52 of Phosphor bronze. The frame and box may be of any suitable metal stamping.

One of the many variations which may be made is by inserting a preselected resistor 70' in a dielectric bolt 32' with one terminal 70a extending through a protrusion 36 to serve as the pin, as illustrated in Fig. 4. The bolt may then be suitably altered to accommodate the resistor, as shown, with the other terminal 70b available to receive the spring pressure and make contact therewith. Preferably, in this variation, the selected resistor is of physical size smaller than standard. The spring is then preferably located to exert its pressure on the other resistor terminal. The remainder of such an arrangement may be similar to that described in connection with the embodiment of Figs. l, 2 and 3. The resistor 70 of Fig. 4 is held so that on complete insertion of the bolt the terminal 7011 just makes contact with the main cable inner conductor, and yet the resistor is free to respond to thespring pressure.

It has been found that when dielectric bolt and pin are pre-asseimbled, cold-flow of the inner main cable dielectric completely. seals the protrusion' when inserted. If, however, the pin is not inserted before the bolt protrusion is forced into the main cable, this cold-flow seals the bore in the protrusion, thereby making it difiicult if not impossible, to afterward insert the pin. The bolt protrusion also affords mechanical support to the sweet pin as it is being inserted and forced through the main cable outer conductor anddielectric.

, It has been found that the connection is rugged, able to withstand far more severe conditions by way of moisture, temperature changes, and the like than it is ever likely to meet. in actual usage, and that its electrical qualities are good. Such connectors have been tested with good results for making branch connections throughout the present television band 'of frequencies, fnom 80 to 210 mc./s.

It will be apparent from the foregoing that the connector of the invention provides a means for making simply and economically an effective branch connection to a coaxial line. a

What is claimed is:

1. In a connector for makinga branch line connection withta coaxialline having spaced inner and outer conductors, the combination comprising a metallic clamp to cradle the said line and .to make contact with said outer conductor on clamping said line, a dielectric bolt in which is carried .coaxially a member having an enlarged body and a metallictpin extending from the body, said bolt having a protrusion surrounding and shielding said enlarged body but leavingthe pin point exposed and having a stop, said clamp having an opening and being arranged to receive said bolt in said opening for forced insertion after the clamp is applied to clamp said line with said stop set to position the pin point at and in contact with the inner conductor of the clamped line and with the protrusion extending through the outer conductor into the spaced between said inner and outer conductors to shield the pin from the said outer conductor, said bolt having an internal chamber in which said enlarged body fits loosely for limited axial movement whereby inadvertent separation of member and bolt is prevented, and yet the member may be spring loaded to insure good contact between the pin and the line inner conductor.

, 2. The connector claimed in claim 1, further comprising a resistor held in said blot, one resistor terminal serving as said pin point and said resistor having a body portion serving as said enlarged body.

3. In a connector for making a branch connection with a coaxial line having spaced inner and outer conductors, the combination comprising a clamp to cradle the said line and having means to' make a connection to the said line outer conductor on clamping the line, an element having at one end thereof a metallic pin with an axis, a portion of said element having dimensions transverse to the pin axis'larger than those of the pin, and a dielectric bolt formed'with an internal chamber receiving said element portion and having a protrusion surrounding and shielding the pin body but leaving substantially only the pin point exposed, said element portion abutting an inner wall of said chamber in one position of the former to prevent movement of said element toward said bolt past a predetermined limit, said clamp receiving the said bolt for forced insertion :of the pin into said line so that the pin point contacts said inner conductor and the protrusion shields the pin from contact with said outer conductor, said chamber receiving said element portion with a loose fit for limited axial movement whereby the element may be spring loaded thereby to spring load the contact of the pin point with the inner conductor.

4. The connector claimed in claim 3, said element being a resistor, said element portion being a resistor body, one of said resistor terminals serving as said pin.

5. The connector claimed in claim 3, said element being metallic, said element portion being the head of the pin.

6. In a connector for making a branch line connection with a coaxial line having spaced inner and outer conductors, the combination comprising a metallic clamp to cradle the said line and to make contact with said outer conductor on clamping said line, a dielectric bolt in which is carried coaxially a member having an enlarged body and a metallic pin extending from the body, said bolt having a protrusion surrounding and shielding said enlarged body but leaving the pin point exposed and having a stop, said clazmp having an opening and being arranged to receive said bolt in said opening for forced insertion after the clamp is applied to clamp said line with said stop set to position the pin point at and in contact with the inner, conductor of the clamped line and with the protrusion extending through the outer conductor into the space between said inner and outer conductors to shield the pin from the said outer conductor, said bolt having an internal chamber in which said enlarged body fits loosely for limited axial movement, said bolt having a bore extending from the said chamber through the bolt head, through which electricalcontact may be made with said enlarged body.

7., The combination claimed in claim 6, the said bore being countersunk at the bolt head portion to receive a resistor body with a'resistor terminal making said contact with said enlarged body.

8. In a coaxial line connector, in combination, a clamping member formed with inner surfaces adapted to grasp the exterior surface of a coaxial line, said member being formed with an aperture which, when said clamping member is in place, is aligned with the inner conductor of said coaxial line; a contact member formed with a conductive pointed end and having one portion of its body enlarged; and a dielectric member having a body portion adapted to fit into said aperture and a tapered end portion, and formed with an internal cavity, said contact member beingmounted in said dielectric memher, the bodypor'tionand tapered end portion of said dielectric member surrounding the enlarged body portion'of the contact 'rnember but leaving its pointed end exposed, said pointed endrextending from the tapered end of said dielectric member, and the enlarged portion of the contact member being located in said cavity, whereby when said clamping member is in place on a coaxial line, said apertureserves as a guide for said dielectric member, and when said dielectric member is forced through said aperture into said line, the tapered end thereof and the pointed end of said contact member pierce the outer conductor of said line and the dielectric material between the inner conductor and outer conduc tor of said coaxial line and said pointed end makes electrical contact with said inner conductor, said tapered portion of said dielectric member shielding said contact member from said outer conductor.

9. In a coaxial line connector as set forth in claim 8, furtherincludingtat least one other contact member having'a pointed end extending from an inner surface of said clamping member of sufiicient length to engage only the outer conductor of said coaxial line when said clamping member is in place on said coaxial line.

10. In a coaxial line connector as set forth in claim 9, said contact member being movably mounted in said dielectric member to permit a limited amount of axial movement thereof relative to said dielectric member, whereby said contact member may be spring biased thereby to spring bias the contact of its pointed end with said inner conductor.

11. In a coaxial line connector as set forth in claim 8, said contact member being movably mounted in said dielectric member to permit a limited amount of axial movement thereof relative to said dielectric member; and further including spring means operatively associated with said contact member for biasing the latter in the direction of the pointed end thereof, for maintaining said pointed end in firm electrical contact with the inner conductor of said coaxial line.

l2. In a coaxial line connector as set forth in claim 11, said dielectric member being formed with an axial aperture therethrough extending from the end thereof opposite said tapered end to the end of said contact member opposite its pointed end; and further including resistor means' having a pair of contact ends, one of said contact ends extending into said aperture .in said dielectric member and making contact with the end opposite said pointed end of said contact member, and the other of said contact ends abutting said spring means and making electrical contact therewith, said resistor serving electrically to isolate said coaxial line and serving also as a mechanical coupling between said spring means and said contact member.

13. In a coaxial line connector as set forth in claim 8, the aperture in said clamping member being internally threaded, and said dielectric member having external threads engageable with said internal threads.

14. In a coaxial line connector as set forth in claim 8, said enlarged portion of the body of said contact member comprising impedance means.

15. In a coaxial line connector, in combination, a clamping member formed with inner surfaces adapted to grasp the exterior surface of a coaxial line, said member being formed with an aperture which, when said clamping member is in place, is aligned with the inner conductor of said coaxial line; contact means formed with a conductive pointed end and having one portion of its body enlarged,

said one portion comprising impedance means; and insulator means including a body portionadapted to fit into said aperture and an end portion of smaller cross-section than said body portion, said body portion being formed with an internal cavity, said contact means being mounted in said insulator means, said pointed end of said contact means forming an extension of said end portion of said insulator means, and the enlarged portion of the contact means being located in said cavity, whereby when said clamping member is in place on a coaxial line, said aperture serves as a guide for said insulator means, and when said insulator means is forced through said aperture into said line, the end portion thereof and the pointed end of said contact means pierce the outer conductor of said line and the dielectric material between the inner conductor and outer conductor of said line and said pointed end makes electrical contact with said inner conductor, said end portion of said insulator means insulating said contact means from said outer conductor.

' 16. A branch line connector for a coaxial line comprising, in combination, clamping means formed with inner surfaces adapted to grasp the external surface of a co-- axial line, said means being formed with an aperture which, when said clamping means is in place, is aligned with the inner conductor of said line; contact means formed with a contact end and having one portion of its body enlarged in cross-section, said enlarged portion of said body comprising impedance means and the remainder of said contact means being formed of a conductor; and dielectric means one portion 'of which fits into said aperture and is formed with a cavity in which the enlarged portion of the contact means is disposed, and another portion of which is of substantially smaller crosssection'than said one portion and forms with the portion of the contact means between the enlarged body thereof and its contact end a tapered coaxial line piercing element, said smaller cross-section portion of said dielectric means surrounding and insulating the contact means between the enlarged body portion thereof and the contact end, but leaving the contact end exposed, whereby when said clamping member is in place on a coaxial line, said aperture serves as a guide for said insulator means, and when said contact end of said contact means is in electrical contact with the inner conductor of said coaxial line, said end portion of said insulator means insulates the contact means from the outer conductor of said coaxial line.

17. A branch line connector for a coaxial line comprising, in combination, clamping means formed with inner surfaces adapted to grasp the external surface of a coaxial line, said means being formed with an internally threaded aperture which, when said contact means is in place, is aligned with the inner conductor of said line; contact means formed with a pointed contact end and including a body portion enlarged in cross-section, said body portion comprising impedance means and the remainder of said contact means being formed of conductive material; and guide means including an outer portion having external threads engageable with the internal threads of-said aperture, a center dielectric portion having a chamber in which said enlarged body portion is located, and an end portion which is of substantially smaller crosssection than said center portion and which surrounds and insulates a portion of the contact means between the enlarged body portion thereof and the pointed contact end, but which leaves the point of the contact end exposed, said end portion of said guide means and the portion of the contact means it surrounds forming together a tapered coaxial line piercing element.

References Cited in the file of this patent UNITED STATES PATENTS 1,067,024 Hall c July 8, 1913 1,435,819 Des Isles Nov. 14, 1922 1,935,313 Feldman Nov. 14, 1933 2,395,373 Johnson Feb. 19, 1946 2,534,786 McElhaney Dec. 19, 1950 2,615,948 Kameu Oct. 28, 1952 2,677,108 Brady Apr. 27, 1954 

